1. Field of the Technology
The present technology relates to a developing device and an image forming apparatus.
2. Description of the Related Art
Copiers, printers, facsimiles, or the like include an image forming apparatus that forms an image by electrophotography. The electrophotographic image forming apparatus forms an electrostatic latent image on a surface of an image bearing member (photoreceptor) using a charging device and an exposure device, develops the electrostatic latent image by supplying developer using a developing device, transfers the developer image on the photoreceptor to a recording medium such as recording paper using a transfer section, and fixes the developer image onto the recording paper using a fixing device and thereby forms an image.
The developer supplied to the photoreceptor by the developing device is contained in a developer tank provided in the developing device. The developer contained in the developer tank is conveyed to a developing roller provided in the developing device. The developing roller rotates while bearing the developer on a surface thereof, and supplies the developer to the photoreceptor. The developer is charged while being conveyed to the developing roller, and the charged developer is moved from the developing roller to the photoreceptor by electrostatic force between the surface of the photoreceptor and the electrostatic latent image. In this manner; the developing device develops the electrostatic latent image on the surface of the photoreceptor, and forms the developer image.
In recent years, accompanying the increase in speed and miniaturization of the image forming apparatus, the decrease in size of a developing device and the increase in developing process speed has been demanded. For example, Japanese Unexamined Patent Publication JP-A 2009-109741 discloses a circulation-type developing device including a developer conveying section that has a first conveying path, a second conveying path, a first communication path, and a second communication path formed by a partition provided inside a developer tank, and that conveys the developer in the first conveying path and the second conveying path in directions opposite to each other. The developer conveying section disclosed JP-A 2009-109741 is an auger screw type member that includes a rotation shaft member having a columnar shape and a spiral blade spirally wound around the rotation shaft member, and developer is circularly conveyed by the developer conveying section and thereby the increase in a developing speed is promoted.
In regard to the developer conveying section disclosed in JP-A 2009-109741, when the size of the developer conveying section is decreased with a shape thereof maintained as it is, the developer conveying section is apt to be bent in a direction orthogonal to an axial line of the rotation shaft member, and as a result, there is a problem in that the developer conveying section and a bottom of a developer tank may come into contact with each other. To avoid this contact, it is necessary to increase the size of the developer tank, such that it is difficult to decrease the size of the entirety of developing device.
In regard to this, when the developer conveying section is configured to have a shape in which the inner diameter of the spiral blade and the outer diameter of the rotation shaft member equal to this inner diameter are increased with the outer diameter of the spiral blade maintained as it is, the strength of the rotation shaft member is increased, and therefore it is possible to suppress the bending. However, when the outer diameter of the rotation shaft member is increased, an occupying volume of the rotation shaft member in the developer tank is increased, and therefore an amount of developer that can be stored in the developer tank is diminished.